In addition to the weapons carried over from MW2, Modern Warfare 3 brings its own set of new weapons for players to use, such as the Karambit. This curved knife is obtainable via the Armory Unlock system; here's how you can get it in MW3.
How to unlock the Karambit Melee weapon in Modern Warfare 3
To get the Karambit melee in MW3 Multiplayer or Zombies, you must reach level 25 so that the Armory Unlock is available to you. From the lobby, press the tab under the daily challenges that says Select New Armory Unlock Challenge (see image). This will open a list of weapons and equipment that you can unlock by completing daily challenges.
Go to the Weapons column, find the Karambit blade, and select Activate as shown in the image above. Once activated, you need to complete five daily challenges to unlock the Karambit permanently. Once you complete all three daily challenges, you just have to get wins in Multiplayer matches to progress. Each win counts as one daily challenge complete.
How to unlock the Karambit via Modern Warfare 3 Zombies
There is another straightforward way of unlocking the Karambit or any new weapon in MWZ. You need to find the knife, equip it in either of your weapon slots, and then exfil with it to unlock it instantly. However, there's no guarantee that you'll find a Karambit in any given Zombies match, so this method may require a few tries. Alternatively, if you have a friend who has unlocked the Karambit, you can ask them to bring it into the Zombies match. Take the knife from them and exfil with it to add it to your armory.
Stay tuned to Pro Game Guides for more Call of Duty: Modern Warfare 3 content. In the meantime, head over to our article on Where to find Quadri Shopping Center in MW3 Zombies.